The invention relates to a device for forming coaxial corrugations in a thin-walled tube.
In the prior art such devices have been proposed comprising a mandril and at least one work forming member into which the wall of the tube may be pressed by a force, and holding jaws arranged around the mandril, of which at least one may be axially displaced during the corrugation forming operation in order to feed the wall into the forming member as the corrugation is being formed.
In one form of such a device designed on these lines, see the U.S. Pat. No. 2,773,538, there was a mandril in the form of a cylindrical head onto which the tube was slipped so as to be positioned within two annular holding jaws, of which pressed the tube against a stationary part of the cylindrical mandril fixed to the frame of the device, while the second holding jaw urged a second part of the tube onto the moving part of the cylindrical mandril. The moving part of the cylindrical mandril was moved together with the second holding jaw axially towards the first holding jaw. Owing to this and the action of internal pressure the tube was pressed outwards into a female forming member (constituted by the holding jaws when they were in engagement with each other) and with the creation of a coaxial corrugation.
Such a device may be used to form coaxial corrugations in hollow cylindrical members relatively quickly when there are no high expectations as regards dimensional accuracy.